AerospaceWeb has said photos of debris are consistent with components of a 757 (see here and here.

Crash scene witnesses

A USA Today article reports the discovery of "scorched bodies of several airline passengers" "still strapped into their seats".

On Tuesday, Army Staff Sgt. Mark Williams witnessed a combat zone for the first time in his 11 years of service. He never imagined it would be inside the Pentagon. One of the first recovery personnel to enter the crippled headquarters building after a hijacked Boeing 757 smashed into it, the urban search-and-rescue specialist found a gruesome sight. "If anyone has ever burned a pot roast, they'll know what the victims looked like," Williams, 30, said Thursday after another 12-hour shift of searching for 190 bodies — those of 126 missing Pentagon personnel and the 64 aboard the doomed jetliner.

The fireball occurred when the jetliner's full fuel tank exploded on impact and roared down corridors so fast that "90% didn't know what happened to them," he said.

Many were sitting at their desks or behind partitions. One woman was found frozen in a sitting position, her arms posed as if reading a document.

Several bodies were found huddled in groups near televisions. Pentagon workers were apparently watching the carnage taking place at the World Trade Center when the hellish scene on TV became reality for them, too.

When Williams discovered the scorched bodies of several airline passengers, they were still strapped into their seats. The stench of charred flesh overwhelmed him.

Personal effects

Personal effects relating to Flight 77 passengers were reported discovered at the scene:

"During an interview earlier this week, Koch delicately handled eerie mementos of the crash found during cleanup: Whittington's battered driver's license... a burnt luggage tag and a wedding ring lie on a book dedicated to those lost in the events of Sept. 11, 2001. The wedding ring belonged to Ruth's daughter and the luggage tag belonged to one her granddaughters."http://onlineathens.com/stories/091104/new_20040911030.shtml

“Suzanne Calley died aboard American Airlines Flight 77 when terrorists hijacked the plane and sent it crashing into the Pentagon... Rescue crews were able to pull Calley’s body from Flight 77’s wreckage.
Jensen [Calley’s husband] spent last year’s anniversary of the national tragedy in Washington, D.C. There, a Pentagon official - assigned to Calley’s family as a liaison - gave Jensen his wife’s wedding ring, which had been recovered from the plane.”http://web.archive.org/web/20060223073358/http://gilroydispatch.com/news/contentview.asp?c=73724

Passenger identification

The Pentagon victims and Flight 77 passengers were identified by DNA:

...all but five of the 184 victims at the Pentagon site were identified months ago...
Families of the airplanes' passengers and crews and those who died within the Pentagon provided DNA samples, typically on toothbrushes or hairbrushes, to aid with identification. The remains that didn't match any of the samples were ruled to be the terrorists, said Chris Kelly, spokesman for the Armed Forces Institute of Pathology, which did the DNA work. The nine sets of remains matched the number of hijackers believed to be on the two planes.http://www.cbsnews.com/stories/2002/08/17/attack/main519033.shtml

Additional work was carried out on the unidentified remains:

Nuclear DNA testing (along with dental records and fingerprints) of the remains from the victims aboard American Airline (AA) Flight 77 and within the Pentagon was useful for identifying 178 of the 183 victims. Five missing individuals (four within the Pentagon and one aboard the airplane) could not be identified due to lack of biological material from the crash. Five remaining nuclear STR profiles were obtained from the crash site that did not match any references for the victims. These profiles were thought to represent the terrorists aboard the flight. The 40 victims aboard the United Airline (UA) Flight 93 that crashed near Shanksville, PA, were also identified by nuclear DNA testing, dental records, and fingerprinting. Four nonmatching nuclear DNA profiles were also obtained from the crash site and again tentatively ascribed to the terrorists.
The DNA results strengthened the hypothesis that two of the terrorists were brothers, as indicated by other evidence. Two of the terrorist STR profiles aboard the AA Flight 77 gave a sibling index greater than 500. To further test the hypothesis of maternal relatedness, AFDIL sequenced the HVI and HVII regions of mtDNA for these individuals. The sequences generated did match in HVI and HVII, which is consistent with a maternal relationship between the two men.http://www.cstl.nist.gov/div831/strbase/pub_pres/Edson2004.pdf

The FBI told us that brothers Nawaf and Salem al-Hazmi were on board Flight 77. Testing reveals two of the DNA profiles appear to be taken from brothers. (See Hijackers DNA profiles.)